In this study, surface compositing of AZ31B magnesium alloy has been investigated using friction stir processing using diverse fillers such as Carbon Nano Tube and Alumina nano particles. Studied parameters were rotation speed (550-1500 rpm), transverse speed (12-44 mm/min), number of passes (1-4), type of filler (CNT, Geraphen, Graphite, Alumina and mixtures of CNT and Alumina), and the weight percent of filler (0-4%). Microhardness, optical metallography, field emission scanning electron microscopy, energy dispersive spectroscopy analysis, tensile and shear-punch tests, XRD analysis, and pin-on-disk wear tests were employed for characterizations of the samples. In the first phase, FSP parameters were investigated and optimized and the accurate range for weight percent of CNT was distinguished. The response in this stage was the hardness of nugget. In phase two, design of experiments (DOE) technique was implemented and investigated ranges became more limited, leading to more precise optimization. ANOVA table for both responses were plotted and the confirmations test were done. Optimized conditions were 24 mm/min, 660 rpm, 4 wt%, and 3 passes by which the responses were 85 Vickers in nugget hardness and 10.2 mg in weight loss. Introduced models predicted the responses well and actual values were very near to the predicted ones. In the third phase the type of filler was changed and four types of fillers (CNT, Graphen, Alumina nano particles, and Graphite) and two hybride types (mixture of CNT and Alumina nano particles) were used. The result showed that the wear and mechanical properties of the sample containing CNT was similar to those of the hybrid sample containing CNT/nano Alumina (2:1 weight ratio). In the fourth phase, the optimized samples in previous phase were characterized. Metallographic studies indicated severe grain refinement in the samples by the grain size reaching to about 2 µm. Wear mechanisms in the samples were a mixture of adhesive, abrasion, oxidation and delamination wear. Tensile fracture represented significant grain refinement and appropriate distribution of particle in the matrix and dimple rupture was the general type of fracture. Sear-punch tests showed 20% increase in shear strength and 10% decrease in elongation. Ultimate tensile strength in nugget zone of the optimized sample was approximately 255 MPa in comparison to 215 MPa for the raw sample. XRD analyses indicated production of no new phase during the process. Key words: Friction Stir Processing, AZ31B Magnesium Alloy, Surface compositing, Carbon Nano Tube, Nano Alumina, Characterization.